We propose to develop an electrical stimulation system with adaptive capabilities for exercise and rehabilitation. The target populations are individuals with: 1) complete spinal cord injury (Sd), 2) post-surgical knee immobilization, and 3) incomplete SCI, traumatic brain injury, or stroke who may regain voluntary motor function through motor retraining therapy. The proposed portable exercise unit will include sensors and an adaptive control algorithm to provide repeatable movements. We anticipate that the adaptive controller will provide safer and more effective exercise than currently available systems. Moreover, the adaptive controller will allow the exercise goals to be defined in movement rather than stimulation-specific parameters. For motor retraining, the system will encourage maximum voluntary effort by providing only the stimulation required to supplement the user about effort. In Phase I, we will: 1) develop a prototype system, 2) perform a limited feasibility test for one subject with complete SCI, and 3) develop and a stimulator for use in Phases II and Ill. In Phase II, exercise benefits will be compared to existing systems, alternate exercise paradigms and target muscles will be evaluated, and application for the secondary and tertiary target populations will be explored. PROPOSED COMMERCIAL APPLICATION: The target price for the proposed system will be $750-$1000. The primary market will includee individuals with complete spinal cord injury (SCI). Alternate markets may include those with post-surgical knee immobilization, or those with incomplete SCI, traumatic brain injury (TBI), or stroke who may benefit from motor retraining therapy.